671
FXUS65 KRIW 271045
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
445 AM MDT Thu Jun 27 2024

.KEY MESSAGES...

- Strong to severe storms today, the main threat being damaging
  wind, though large hail may also occur.

- Elevated fire weather conditions Friday through Sunday. Sunday looks
  to be the windiest and driest of those days. Hot Sunday.

- Weather system moves through late Sunday through Monday,
  bringing cooler temperatures and precipitation chances, though
  mainly across northern Wyoming.

&&

.DISCUSSION...
Issued at 119 AM MDT Thu Jun 27 2024

The main weather story for today is the scattered thunderstorm
chances, with strong to severe storms. An upper-level trough moving
eastward over the Washington/Canada border brings a cold front
through the area today. This feature brings good CAPE values (up to
1000 J/kg) as well as decent shear (pockets of 30 to 45 kt 1-6km and
20 to 30 kt 0-1km) ahead of it. The high that has been sitting south
of the state continues to rotate moisture around it, with morning
and afternoon dewpoints in the upper 40s to lower 50s. All these
factors favor strong to severe thunderstorms this afternoon across
much of the area. Generally, the main threat occurs between 11am and
8pm MDT, with the strongest storm potential in the afternoon as peak
heating takes place. The main threat is damaging outflow winds,
though large hail is also possible with stronger storms. High-
resolution models are supporting discrete cells, with supercells
possible. A tornado cannot be ruled out, with the most favored area
being southern Sweetwater County and areas east-northeast of our
CWA. Well-above average precipitable water (PWAT) values means heavy
rain can occur with any storm. Good upper level flow should keep
storms moving, though training of storms would be the main flooding
risk; models again show this threat to mainly occur south of I-80 in
Sweetwater County. The Storm Prediction Center (SPC) has all but far
western portions of the area in a slight risk (2 of 5) today, with
wind being the main threat, though also highlighting a hail threat.
Storms come to an end this evening.

Friday looks dry for most. Some lingering moisture brings isolated
(15% to 30%) shower and thunderstorm chances across southern
Sweetwater County to near Casper Mountain and across the northern
mountains. High temperatures are a bit cooler in the wake of the
front, with highs in the middle to upper 70s for most, or cooler
than average for late June. Relative humidity (RH) values drop near,
to below, 15% Friday afternoon. A tight pressure gradient brings
afternoon winds gusting 25 to 25 mph for many. As a result, elevated
fire weather conditions occur.

Dry conditions continue Saturday, with elevated fire weather
conditions continuing, though will be more marginal as winds are
expected to be less. Sunday ramps up the fire concerns, however. An
approaching system increases winds once again, with gusts over 30
mph for many locations. Very dry air brings RHs under 15% for most
of the area, with under 10% for many locations. Temperatures will
also be hot, being about 8 to 15 degrees above average. Rain chances
pick up, mainly over the northwest mountains as the system
approaches Sunday afternoon and evening.

Monday looks cooler as the associated front passes through Sunday
night. Shower and storm chances also continue through the day;
current model projections favors these chances across northern
Wyoming. Past Monday, temperatures look to be a bit above average
through the end of the workweek, with little in the way of rain
chances as a high builds over the western U.S.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 445 AM MDT Thu Jun 27 2024

Widely scattered showers continue across the forecast area this
morning. However, impacts remain minimal. A low pressure system
will move over the Northern Rockies through the day today,
which will lead to the development of scattered rain showers and
thunderstorms through the afternoon. Some of the thunderstorms
will be strong to possibly severe. As it stands right now, KRKS
has the best chance of prevailing TSRA, but not a high enough
chance to add it to this issuance of the TAFs. There`s a slight
chance (20- 30%) of thunderstorms at all terminals Thursday
afternoon. Wind will begin to increase after 15Z for most
terminals, with gusts of 25-30 knots prevalent across the area.
Higher gusts are likely (70%) with thunderstorm downdrafts/outflows.
There will be prevailing VFR conditions, with temporary drops
to MVFR/IFR if a thunderstorm moves directly over the terminal.
The threat for thunderstorms will begin to wane after 00Z, with
any lingering showers/thunderstorms ending across the area by
06Z.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Wittmann
AVIATION...LaVoie